Here is a brief restatement of the vision of the great chain of being. I've put the various claims comprising the vision into logical order to show that they form a single, large argument.

I include references to Descartes, Spinoza, and Leibniz in order to lead you to texts which clarify and amplify these propositions. I have indented these references out of the way to allow you read the main propositions without distraction.

The top of the chain represents perfection in the highest degree. Most believers in the chain call this God.

The chain in its entirety represents all degrees of perfection from the highest and fullest to the lowest and least; it is complete.

Similarly, evil is not something positive; good is. Evil is the lack of good; evil is privation.

Descartes, Meditations 114.5, 116.5.

Leibniz, Discourse §§ 4, 30.

In general, being or existence is a perfection; to be is more perfect than not to be. What has positive existence is good and was created by God; what is privation lacks being and goodness, and was not created at all.

It follows (from principle 11) that the idea of the being with all perfections is the idea of an existing being. This is the ontological argument for the existence of God.

Descartes, Discourse 27.8; Meditations 107.3, 121.5.

Spinoza, Ethics 31 (I defs 1, 3, 6), 37.2 (I.11), 46.9 (I.20)

Leibniz, Discourse § 23; Monadology §§ 40, 44.

It follows (from principle 9) that for propositions, truth is the default; and (from principle 11) that for entities, existence is the default. If a proposition's truth is possible, we may assume that it is actually true, and if an entity's existence is possible, we may assume that it actually exists, unless there are special reasons to think not. Proofs of truth and existence tend to follow from possibility alone; the burden of proof is on the denial of truth or existence.

Hence, the things in the middle of the chain are dependent or contingent. (The nothingness at the bottom is dependent in the sense that nothingness depends on the contrast with somethingness.)

The being at the top of the chain is utterly independent or self-sufficient or absolute.

Descartes, Meditations 104.3, 106.3.

Spinoza, Ethics 31 (I defs 1, 3, 6), 44.2 (I.17), 56.5 (I.33 sch.2).

Leibniz, Monadology § 40.

If A causes B, then B depends on A. Hence (by principle 14 above) B is less perfect than A. Therefore a cause must be more perfect than its effect.

Descartes, Discourse 26.3; Meditations 96-97.

Leibniz, Monadology § 50.

Dependent beings, therefore, depend on more perfect causes than themselves, which in turn depend on more perfect causes themselves, and so on, until the series comes to an end with the most perfect, uncaused (or self-caused), independent being, which is at the top of the chain.

Descartes, Meditations 106.3.

Leibniz, Monadology §§ 36, 40, 45.

It follows that, if there are any dependent beings (for example, ourselves), then there must be an independent, hence perfect or absolute being (God). This is the cosmological argument for the existence of God.

Spinoza, Baruch. Ethics, Treatise on the Emendation of the Intellect, and Selected Letters. Trans. Samuel Shirley and Seymour Feldman, Hackett, 1992. In addition to page numbers from this edition, I cite Spinoza's propositions in the Ethics by number.